HXHV virus, nucleic material, peptide material and uses

ABSTRACT

Isolated HXHV virus having the following characteristics:
         (i) a DNA genome which is at least partially single-stranded,   (ii) the said genome comprises one reading frame (ORF) encoding one protein or one polyprotein   (iii) the said genome comprises a nucleotide sequence which exhibits, for any segment of at least 40 nucleotides belonging to the said sequence, at least 90% homology with SEQ ID NO: 1 or with its complementary sequence,
 
nucleic material and peptide material and uses.

Hepatitis is the most important of the transmissible diseases. The mode of transmission is most often transfusion, organ transplants and haemodialysis, but hepatitis can also be transmitted by ingestion of contaminated food or water and by contact between individuals.

Viral hepatitis are induced by various viral agents which are distinguishable from each other by their genomes and their modes of replication. Viral hepatitis cause damage to the liver with varying degrees of severity. More than a billion people worldwide suffer from viral hepatitis. Serious risks exist in the chronic forms of hepatitis which can progress to cirrhosis or hepatocarcinoma. Viral hepatitis can be diagnosed by the detection of well-defined symptoms, such as jaundice, high levels of transaminases (aspartate transaminase or AST, alanine transaminase or ALT, lactate dehydrogenase or LDH), and hepatic lesions. Despite the knowledge of various hepatitis A, B, C, D, E, G and TTV viruses, 5% of all hepatitis and 40% of fulminant hepatitis remain unexplained, hence the hypothesis of the existence of unknown hepatitis viruses. These hepatitis of unknown aetiology are both post-transfusional and sporadic, chronic or fulminant. They are commonly called hepatitis X.

Hepatitis G (GBV-A, GBV-B, GBV-C) and TTV viruses recently identified do not appear to be pathogenic in humans and cannot therefore explain the cases of hepatitis of unknown aetiology or hepatitis X.

From one case of serious hepatitis of unknown aetiology, in a patient in whom a treatment with interferon made it possible to normalize transaminases, the present inventors were able to clone, by means of the “RDA” (Representational Difference Analysis) subtractive hybridization technique, the nucleic acids differentially expressed between the serum at the transaminase peak and the serum after normalization of the transaminases. 643 clones representing DNA sequences specific to serum at the transaminase peak were screened. In order to exclude the possibility of homologies with the human genome or any other known sequence, various routes were explored:

-   -   hybridization of the 643 clones with a “human genomic DNA”         sonde, which made it possible to show that 593 clones hybridize         with the “human genomic DNA” probe and that 50 clones do not         hybridize with the “human genomic DNA” probe and comprise an         insert,     -   search in the data banks for possible homologies between the         sequences of these 50 clones and the published sequences, using         the BLAST program at the NCBI site according to the parameters         given by the site,     -   additional screening of 4 clones selected from the preceding         step by “Dot blot” on the DNA of the clones selected using a         radioactively labelled “human genomic DNA” probe and by Southern         blotting of human genomic DNA using, as probe, the radioactively         labelled clones selected.

At the end of these various steps, 2 DNA clones were selected of which the sequences were unknown in data banks. By virtue of PCRs performed within the cloned sequences, tested on human genomic DNA obtained from blood donors, in the end a single clone containing an insert of 1400 base pairs was selected for its lack of homology with the human genomic DNA and with any sequences present in the data banks. The sequence of this clone was called XH. This sequence is rich in GC (62%) and has four open reading frames. This isolated sequence was then characterized by four parallel studies:

-   -   bioclinical and epidemiological study,     -   molecular study,     -   production of specific antibodies,     -   electron microscopy study.

The results show that:

-   -   the XH sequence is found by PCR by means of specific primers in         10% of patients carrying a chronic hepatitis of unknown         aetiology present in the study (out of 110 patients tested),     -   this sequence is absent from the blood donors tested by the same         PCR specific for the cloned XH sequence,     -   this sequence is a DNA sequence which is at least partially         single-stranded,     -   it has several reading frames and one of the reading frames         encodes a protein of 21 kD, which protein possesses a region         which exhibits all the immunogenicity and hydrophilicity         properties required to induce the production of antibodies,     -   fractionation on sucrose gradients of a serum of a patient         non-A-E positive by PCR for the XH sequence (XH+) made it         possible to isolate two consecutives fractions (1.3-1.5 g/cm³)         positive for the XH sequence in which were detected particles         whose size and regularity are compatible with those of a viral         agent. These particles are not observed in the gradient         fractions negative by PCR for the XH sequence. This novel         infectious agent was called HXHV.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a graph of results of ELISA test using SEQ ID NO:6 for the capture of antibodies specific for the HXHV virus potentially present in patients having chronic non-A, non-E hepatitis.

DETAILED DESCRIPTION OF EMBODIMENTS

Accordingly, the present invention relates to the isolated HXHV virus and provides nucleic acids and polypeptides which are capable of being derived from HXHV. Furthermore, the invention provides the means for diagnosing an HXHV virus infection in patients or animals suspected of having a viral hepatitis and the pharmaceutical or vaccine compositions for preventing or treating the disease associated with the infection.

Thus, the present invention relates to

-   -   the isolated HXHV virus exhibiting the following         characteristics:     -   (i) a DNA genome which is at least partially single-stranded,     -   (ii) the said genome comprises one or more reading frames (ORF)         encoding one or more proteins or polyproteins;     -   (iii) the said genome comprises a nucleotide sequence capable of         hybridizing with the sequence SEQ ID NO: 1 or with the sequence         complementary to SEQ ID NO: 1; preferably, it has a nucleotide         sequence which exhibits, for any segment of at least 40         nucleotides belonging to the said sequence, at least 90%,         advantageously at least 95%, or better still at least 98%,         homology with SEQ ID NO: 1 or with its complementary sequence;     -   a nucleic acid sequence capable of being obtained from the         genome of the HXHV virus or fragments of the said genome or a         nucleic acid sequence homologous to the said nucleic acid         sequence SEQ ID NO: 1 or to the sequence complementary to SEQ ID         NO: 1, and exhibiting at least 90%, preferably at least 95%, and         advantageously at least 98%, homology over the length of the         sequence represented in SEQ ID NO: 1; the virus having the         characteristics defined above;     -   a DNA or RNA nucleotide fragment comprising or consisting of a         DNA or RNA nucleotide sequence of at least 12 contiguous         nucleotides, preferably of at least 15 or 18 contiguous         nucleotides, and advantageously of at least 21 contiguous         nucleotides, of the DNA nucleotide sequence SEQ ID NO: 1 or of a         nucleotide sequence which exhibits at least 90%, for example at         least 95% or 98% homology with respect to the sequence         represented in SEQ ID NO: 1 or of their complementary DNA         sequences or of the product of transcription of the said DNA         nucleotide sequences; in particular, a fragment in which the         said contiguous nucleotides belong to one of the following         segments: a segment whose sequence starts at nucleotide 813 and         ends at nucleotide 1361 of SEQ ID NO: 1 and a segment whose         sequence starts at nucleotide 927 and ends at nucleotide 968 of         SEQ ID NO: 1, the complementary fragment and the product of         transcription of the said fragments and a fragment comprising or         consisting of SEQ ID NO: 1 or its complementary DNA sequence or         a sequence which is the product of transcription of SEQ ID NO:1;     -   a DNA molecule which comprises or consists of a DNA nucleotide         sequence represented in SEQ ID NO: 1 or in that it comprises at         least one DNA nucleotide fragment as defined above or their         complementary sequences;     -   an RNA molecule which comprises or consists of an RNA nucleotide         sequence which is the product of transcription of a DNA         nucleotide sequence represented in SEQ ID NO: 1 or of at least         one of its fragments as defined above or their complementary         sequences.

The above homology covers the functional equivalents of the sequence SEQ ID NO: 1, that is to say the DNA sequences in which at least one codon can be replaced by another codon while encoding an identical amino acid. This is referred to as degeneracy of the genetic code. Thus, the codes for argininine, for serine and for leucine exhibit a degeneracy of the order 6 (that is to say that there are six different codons for each of them), whereas the codes for the other amino acids, such as glutamic acid, glutamine, tyrosine, histidine and a few others exhibit a degeneracy of the order 2. Of all the amino acids, only tryptophan and methionine have a degeneracy of the order 1. It is therefore clear that for the expression of a polypeptide whose sequence is for example represented in SEQ ID NO: 6, it is possible to use variants and functional nucleic acid sequences in which the codon compositions are different from the nucleic acid sequence represented in SEQ ID NO: 1.

The homology defined above also relates to the mutants of the HXHV virus, and in particular those derived from natural variability. Indeed, it is well known to specialists that the viruses have relatively high levels of spontaneous or induced mutations.

The invention also relates to

-   -   a polypeptide comprising a polypeptide sequence or at least one         of its fragments, characterized in that the said polypeptide         sequence is encoded by the genome of the HXHV virus or by         fragments of the said genome, or by their functional equivalents         or by a nucleotide sequence which exhibits at least 90%         homology, preferably at least 95% homology and advantageously at         least 98% homology with respect to the sequence represented in         SEQ ID NO: 1 and in that the virus has the characteristics         determined above;     -   a polypeptide fragment, characterized in that it comprises or         consists of a peptide sequence of at least 4 amino acids,         preferably of at least 5 or 6 amino acids and advantageously of         at least 7 amino acids, preferably still of at most 15 amino         acids, in particular from 6 to 15 amino acids and advantageously         from 6 to 10 or from 8 to 12 amino acids of the peptide sequence         represented in SEQ ID NO: 5 or of a peptide sequence         functionally equivalent to SEQ ID NO: 5. The inventors have in         particular shown that in the sequence SEQ ID NO: 5, there is a         region of 14 amino acids which exhibits all the required         immunogenicity and hydrophilicity properties required to induce         a humoral response. This polypeptide of 14 amino acids is         identified in SEQ ID NO: 6. They have also shown that this         polypeptide of 14 amino acids corresponds to an antigenic region         of the sequence represented in SEQ ID NO: 5 since it has made it         possible to develop an ELISA test protocol for the detection of         anti-HXHV antibodies in patients having chronic non-A non-E         hepatitis; an advantageous polypeptide fragment comprises or         consists of SEQ ID NO: 6 or a polypeptide sequence functionally         equivalent to SEQ ID NO: 6;     -   a polypeptide fragment which comprises or which consists of a         peptide sequence represented in SEQ ID NO: 5 or a peptide         sequence functionally equivalent to SEQ ID NO: 5.

“Polypeptide” denotes a peptide, in the isolated state, having a succession of a variable number of amino acids, such as an oligopeptide, a protein, a fusion protein, a fusion peptide, a synthetic peptide. A polypeptide may be obtained by various techniques well known to a person skilled in the art, and in particular by chemical synthesis or by genetic recombination techniques. The polypeptides according to the invention may be obtained by conventional methods of synthesis, for example with an automated peptide synthesizer, or by genetic engineering techniques comprising the insertion of a DNA sequence encoding the said polypeptide into an expression vector such as a plasmid or a virus, and the transformation of cells with this expression vector and culturing of these cells.

The expression peptide sequence equivalent to a reference peptide sequence is understood to mean an amino acid sequence modified by insertion and/or deletion and/or substitution and/or extension and/or shortening and/or chemical modification of one or more amino acids, as long as these modifications substantially preserve or even develop the immunoreactive properties of the said reference peptide sequence.

Thus, the expression functionally equivalent sequences which preserve the immunoreactive properties of SEQ ID NO: 5 is understood to mean in particular the sequences in which one or more amino acids are substituted by one or more other amino acids; the sequences in which one or more amino acids of the L series are replaced by an amino acid of the D series, and vice versa; the sequences into which a modification of the amino acid side chains is introduced, such as an acetylation of the amine functional groups, a carboxylation of the thiol functional groups, an esterification of the carboxylic functional groups; a modification of the peptide bonds such as for example of the carba, retro, inverso, retro-inverso, reduced and methyleneoxy bonds.

For example, one or more amino acids in the sequences of the polypeptides of the invention may be substituted by one or more other amino acids of similar polarity which act as functional equivalents. Substitutions for an amino acid in polypeptide sequences of interest may be determined from other members of the class to which the amino acid belongs. For example, the nonpolar (hydrophobic) amino acids comprise alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan and methionine. The polar neutral amino acids comprise glycine, serine, threonine, cysteine, tyrosine, asparagine and glutamine. The positively charged (basic) amino acids comprise arginine, lysine and histidine. The negatively charged (acidic) amino acids comprise aspartic acid and glutamic acid. Other substitutions for an amino acid in polypeptide sequences of interest may be determined from the information contained in the article by Kramer A. et al. (Molecular Immunology, Vol. 32, No. 7, pp. 459-465 (1995)). These authors have set up banks in which, in order to reduce the problem of combinatory explosion of the number of molecules, they used groups of amino acids consisting of amino acids having similar physicochemical properties and it is the amino acids grouped together in each of these six groups, listed below, which are considered mainly as equivalents in the present invention.

-   -   Group 1: alanine, proline, glycine.     -   Group 2: aspartic acid, glutamic acid.     -   Group 3: histidine, lysine, arginine.     -   Group 4: asparagine, glutamine, serine, threonine.     -   Group 5: phenylalanine, tyrosine, tryptophan.     -   Group 6: isoleucine, leucine, valine, methionine.

The equivalence for a peptide sequence with respect to a reference peptide sequence may be defined by its identity or its homology, expressed as a percentage, with the said reference sequence. This percentage is determined, for a sequence of a given number of contiguous amino acids, by alignment of the two sequences, moving one with respect to the other, and comparing the amino acids in the two sequences. The percentage of identity is determined from the number of amino acids which are identical to the amino acids of the reference sequence, in the same position. The percentage homology is determined from the number of amino acids which are equivalent to amino acids of the reference sequence, in the same position.

The invention also relates to an expression cassette which is functional in a cell derived from a prokaryotic or eukaryotic organism allowing the expression of a nucleic acid sequence or of a DNA fragment or of a DNA molecule as described above, placed under the control of elements necessary for its expression. The expression cassette is characterized in that it is functional in a cell derived from a prokaryotic organism, in particular E. coli, or from a eukaryotic or lower eukaryotic organism, in particular COS and CHO cells and Saccharomyces cerevisiae and Pichia pastoris cells.

The invention also relates to a vector comprising the said expression cassette; a cell derived from a prokaryotic organism, such as E. coli or a eukaryotic organism, preferably a eukaryotic or lower eukaryotic organism, and advantageously a COS or CHO cell or a cell derived from Saccharomyces cerevisiae or Pichia pastoris comprising an expression cassette or a vector as defined above; and the polypeptide produced by the expression cassette, the vector or the cell.

The subject of the invention is a method for preparing a polypeptide or a polypeptide fragment as defined above which consists in cultivating a host cell satisfying the preceding definitions, in an appropriate culture medium, the said host cell being transformed with an expression vector which contains a DNA nucleic acid sequence as defined above or a DNA nucleic fragment as defined above or a DNA molecule as defined above, and in purifying the said polypeptide produced to a required degree of purity.

The subject of the invention is also an immunogenic polypeptide, characterized in that it has a peptide sequence or in that it consists of a polypeptide as defined above, in particular the polypeptide represented in SEQ ID NO: 6. Such an immunogenic polypeptide is used for the production of monoclonal or polyclonal antibodies or of fragments of the said antibodies and the invention encompasses the monoclonal or polyclonal antibodies or fragments thereof, being obtained by immunizing a mammalian animal (rabbit, rat, mouse) with such an immunogenic peptide.

The production of monoclonal or polyclonal antibodies is well known to a person skilled in the art. There may be mentioned by way of reference Köhler G. and Milstein C. (1975): Continuous culture of fused cells secreting antibody of predefined specificity, Nature 256:495-497 and Galfre G. et al. (1977) Nature, 266: 522-550 for the production of monoclonal antibodies and Roda A., Bolelli G. F.: Production of high-titer antibody to bile acids, Journal of Steroid Biochemistry, Vol. 13, pp 449-454 (1980) for the production of polyclonal antibodies. Antibodies may also be produced by immunizing mice, rats or rabbits with the HXHV viral particles. For the production of polyclonal and monoclonal antibodies, the immunogen may be coupled to serum albumin (peptide SA) or to Keyhole Lympet haemocyanin (peptide KLH) as support for the immunization. In the context of the present invention, the immunogen identified in SEQ ID NO: 6 is coupled to BSA (bovine serum albumin). The animals are subjected to several injections of immunogen, the antibodies are collected from the serum, purified (brought into contact with a “normal” liver powder) and are then screened for their specificity using the usual techniques, such as ELISA or Western blot tests. For the production of monoclonal antibodies, the animals are subjected to an injection of immunogen using Freund's complete adjuvant. The sera and the hybridoma culture supernatants obtained from the immunized animals are analysed for their specificity and their selectivity using conventional techniques, such as for example ELISA or Western blot tests. The hybridomas producing the most specific and the most sensitive antibodies are selected. Monoclonal antibodies may also be produced in vitro by cell culture of the hybridomas produced or by recovering ascitic fluid, after intraperitoneal injection of the hybridomas into mice. Regardless of the mode of production, as a supernatant or as an ascitic fluid, the antibodies are then purified. The methods of purification used are mainly filtration on an ion-exchange gel and exclusion chromatography or affinity chromatography (protein A or G). A sufficient number of antibodies are screened in functional tests for identifying the most efficient antibodies. The in vitro production of antibodies, of antibody fragments or of antibody derivatives, such as chimeric antibodies produced by genetic engineering, is well known to persons skilled in the art. It is advantageous to use humanized antibodies. The “humanized” forms of nonhuman antibodies, for example murine antibodies, are chimeric antibodies which comprise a minimal sequence derived from a nonhuman immunoglobulin. For the majority, the humanized antibodies are human immunoglobulins (receptor antibody) in which the residues of a hypervariable region of the receptor are replaced by residues of a hypervariable region of a nonhuman donor species (donor antibody), such as mice, rats, rabbits or nonhuman primates, having the desired specificity, affinity and capacity. In some cases, the residues (FR) of the Fv region of the human immunoglobulin are replaced by corresponding nonhuman residues. Furthermore, the humanized antibodies may comprise residues which are not found in the recipient antibody or in the donor antibody. These modifications are performed in order to improve the performance of the antibody. In general, the humanized antibody will comprise at least, and preferably, two variable domains, in which all or nearly all the hypervariable loops correspond to a nonhuman immunoglobulin and all or nearly all the FR regions will be those of a human immunoglobulin. The humanized antibodies may optionally also comprise at least part of a constant (Fc) region of an immunoglobulin, such as a human immunoglobulin (Jones et al., Nature 321: 522-525 (1986); Reichmann et al., Nature 332: 323-329 (1988); and Presta et al., Curr. Op. Struct. Biol. 2: 593-596 (1992).

More particularly, the expression antibody fragment is understood to mean the F(ab)2, Fab, Fab′, sFv fragments (Blazar et al., 1997, Journal of Immunology 159: 5821-5833 and Bird et al., 1988, Science 242: 423-426) of a native antobidy and the expression derived is understood to mean, inter alia, a chimeric derivative of a native antibody (see for example Arakawa et al., 1996, J. Biochem 120: 657-662 and Chaudray et al., 1989, Nature 339: 394-397). These antibody fragments and antibody derivatives preserve the capacity to selectively bind to the target antigen.

The monoclonal or polyclonal antibody thus obtained or its fragment is incorporated into a diagnostic composition which is used in a method for detecting at least one polypeptide or one polypeptide fragment as defined above in a biological sample, according to which the biological sample is brought into contact with the composition under predetermined conditions which allow the formation of antibody/antigen complexes and the formation of the said complexes is detected.

The subject of the invention is also a diagnostic composition which comprises a polypeptide or a polypeptide fragment as defined above and a method for detecting antibodies directed against the HXHV virus or at least against a polypeptide or a polypeptide fragment of the invention, according to which a biological sample suspected of being or of having possibly been infected with the HXHV virus is brought into contact with the diagnositic composition under predetermined conditions which allow the formation of antibody/antigen complexes and the formation of the said complexes is detected. The method described in the experimental part of the appended figure clearly shows that the polypeptide of the invention or the polypeptide fragment SEQ ID NO: 6 makes it possible to detect antibodies specific for the HXHV virus in patients having a non-A, non-E hepatitis.

It is known that during an infection by a viral agent, the host develops antibodies directed against this viral agent (humoral response). It is shown in the experimental part that the immunization of rabbits with an immunogen of the invention allows the producction of antibodies by the rabbits. It has also been shown that patients having a non-A, non-E hepatitis developed antibodies directed against the HXHV virus. The subject of the present invnetion is therefore also the biological material for the preparation of a pharmaceutical composition intended for the treatment of human beings or of animals infected with at least the HXHV virus and immunogenic preparations which may be used to produce therapeutic vaccines against an HXHV virus infection and prophylactic vaccines for preventing a potential HXHV virus infection, the said immunogenic preparations comprising:

(i) either at least one natural, recombinant or synthetic polypeptide or polypeptide fragment of the invention; or

(ii) the HXHV virus, for example in an attenuated or mutated form.

The subject of the present invention is also the use of at least one monoclonal or polyclonal antibody or of at least one fragment of the said antibodies of the invention, specific for at least one polypeptide or a polypeptide fragment as defined above in (i) for the preparation of a pharmaceutical composition which, when administered to a patient infected with the HXHV virus, has the capacity to reduce or even inhibit the proliferation and/or replication of the virus. These antibodies or fragments thereof are called neutralizing antibodies.

Consequently, the invention relates to an immunogenic or vaccine composition, characterized in that it comprises a polypeptide or a polypeptide fragment of the invention or the HXHV virus, optionally combined with an appropriate vehicle and/or adjuvant and/or diluent and/or with a pharmaceutically acceptable excipient; and to a pharmaceutical composition comprising a biological material as defined above, optionally combined with an appropriate vehicle and/or adjuvant and/or diluent and/or with a pharmaceutically acceptable excipient.

The expression biological sample is understood to mean for example blood, serum, plasma, tissue samples, such as liver biopsy extracts.

The vaccines prepared are injectable, that is to say in liquid solution or in suspension. Optionally, the preparation may also be emulsified. The antigenic molecule may be mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredient. Examples of favourable excipients are water, a saline solution, dextrose, glycerol, ethanol or equivalents and combinations thereof. If desired, the vaccine may contain minor quantities of auxiliary substances such as wetting or emulsifying agents, pH-buffering agents or adjuvants such as aluminium hydroxide, the muramyl dipeptide or variations thereof. In the case of peptides, their coupling to a larger molecule (KLH, tetanus toxin) sometimes increases immunogenicity. The vaccines are conventionally administered by injection, for example intramuscularly. Additional favourable formulations with other modes of administration include suppositories and sometimes oral formulations.

The expression “pharmaceutically acceptable vehicle” is understood to mean carriers and vehicles administrable to human beings or to an animal, as described for example in Remington's Pharmaceutical Sciences 16^(th) ed., Mack Publishing Co. The pharmaceutically acceptable vehicle is preferably isotonic, hypotonic or has low hypertonicity and a relatively low ionic strength. The definitions of pharmaceutically acceptable excipients and adjuvants are also given in Remington's Pharmaceutical Sciences cited above.

The subject of the invention is also

-   -   a probe, characterized in that it is capable of hybridizing,         under defined stringency conditions, with a nucleic acid         sequence or with a DNA or RNA nucleotide fragment or with a DNA         or RNA molecule of the invention; preferably, a probe of the         invention comprises at least 12 nucleotides, and the         hybridization is carried out under stringency conditions         corresponding to a combination of the temperature and the salt         concentration chosen approximately between 12 and 20° C. under         the Tm (“melting temperature”) of the probe/nucleotide sequence         complex to be detected;     -   a primer, characterized in that it is capable of hybridizing,         under defined stringency conditions with a nucleic acid sequence         or with a DNA or RNA nucleotide fragment or with a DNA or RNA         molecule of the invention preferably, a primer of the invention         comprises at least 12 nucleotides, and the hybridization is         carried out under stringency conditions corresponding to a         combination of the temperature and the salt concentration chosen         approximately between 12 and 20° C. under the Tm (“melting         temperature”) of the primer/nucleotide sequence complex to be         amplified and/or detected;     -   a primer capable of hybridizing with a nucleic sequence or with         a nucleotide fragment or with a DNA molecule of the invention,         characterized in that it is chosen from any of the sequences SEQ         IDs NO: 19 to 22;     -   an anti-nucleic acid antibody, characterized in that it is         capable of binding to a nucleic acid sequence or to a DNA or RNA         nucleotide fragment or to a DNA or RNA molecule;     -   a diagnostic composition, characterized in that it comprises at         least one probe or one primer or one anti-nucleic acid antibody         as defined above;     -   a method for detecting viral DNA and/or RNA, according to which         a sample is collected from a patient, the said sample is treated         if necessary in order to extract the DNA and/or the RNA         therefrom, the said sample is brought into contact with at least         one probe or one primer of the invention, under defined         stringency conditions and the presence of viral DNA and/or RNA         in the sample is detected either by demonstrating a         hybridization of the said viral DNA and/or RNA with at least one         probe, or by amplification of the said DNA and/or RNA; and     -   a method for detecting viral DNA and/or RNA, according to which         a serum or plasma sample is collected from a patient, the said         sample is treated if necessary in order to extract the DNA         and/or RNA therefrom, the said sample is brought into contact         with at least one anti-nucleic acid antibody, the said antibody         being optionally labelled with any appropriate marker and the         formation of a nucleic acid/antibody complex is demonstrated.

The production of polynucleotides, probes or primers forms part of the general knowledge of persons skilled in the art. There may be mentioned in particular the use of restriction enzymes, and chemical synthesis on an automated synthesizer. The probes and primers capable of hybridizing, under determined stringency conditions, with a DNA or RNA nucleotide sequence or with a nucleotide fragment as defined above form part of this definition. It is within the capability of persons skilled in the art to define the appropriate stringency conditions. Characteristic stringency conditions are those which correspond to a combination of the temperature and of the salt concentration chosen approximately between 12 and 20° C. under the Tm (“melting temperature”) of the hybrid to be studied. Reference may thus be made to the book by George H. Keller et Mark M. Manak, DNA PROBES, second edition, Stockton Press, 1993, 49 West 24^(th) St., New York, N.Y. 10010 USA. The stringency conditions for differentiation of even a single point mutation have been known since at least the period 1979; there may be mentioned by way of examples Wallace R. B et al., DNA. Nucleic. Acids. Res. 6, 3543-3557 (1979), Wallace R. B et al., Science, 209, 1396-1400 (1980), Itakura K. and Riggs A. D., Science, 209, 1401-1405 (1980), Suggs S. V. et al., PNAS, 78, 6613-6617 (1981), Wallace R. B et al. DNA. Nucleic. Acids. Res., 9, 3647-3656 (1981), Wallace R. B et al. DNA. Nucleic. Acids. Res., 9, 879-894 (1981) et Conner B. J. et al, PNAS, 80, 278-282 (1983). Moreover, techniques are known for the production of anti-nucleic acid antibodies. There may be mentioned, by way of examples, Philippe Cros et al., Nucleic Acides Researc, 1994, Vol. 22, No. 15, 2951-2957; Anderson, W. F. et al. (1988) Bioessays, 8 (2), 69-74; Lee, J. S. et al. (1984) FEBS Lett., 168, 303-306; Malfoy, B. et al. (1982) Biochemistry, 21(22), 5463-5467; Stollar, B. D. et al., J. J. (eds) Methods in Enzymology, Academic Press, pp 70-85; Traincard, F. et al. (1989) J. Immunol. Meth., 123, 83-91 and Traincard, F. et al. (1989) Mol. Cell. Probes, 3, 27-38).

The invention also relates to:

-   -   a vaccine composition comprising a DNA sequence encoding at         least one polypeptide or one polypeptide fragment of the         invention, the said DNA being mixed with an appropriate vehicle         and/or diluent;     -   an anti-sense or anti-gene oligonucleotide, characterized in         that it is capable of specifically interfering with the         synthesis of at least one polypeptide or one polypeptide         fragment of the invention;     -   a pharmaceutical composition, characterized in that it comprises         at least one anti-sense oligonucleotide or one anti-gene         oligonucleotide;     -   a vector, characterized in that it comprises at least one gene         of therapeutic or vaccine interest, the said gene encoding in         particular     -   (i) either at least one polypeptide or one polypeptide fragment         of the invention;     -   (ii) or at least all or part of a polyclonal or monoclonal         antibody capable of binding to at least one polypeptide or         polypeptide fragment defined in (i);     -   (iii) or at least one molecule inhibiting at least one         polypeptide or polypeptide fragment defined in (i);     -   (iv) or at least one ligand or any part of a ligand capable of         binding to at least one polypeptide or polypeptide fragment         defined in (i) and/or of inhibiting its function;     -   a therapeutic or vaccine composition, characterized in that it         comprises, inter alia, a vector as defined in Claim 10 and in         that the said gene of interest is placed under the control of         elements ensuring its expression in vivo;     -   a biological material for the preparation of a pharmaceutical or         vaccine composition, comprising at least one cell, in particular         a cell not naturally producing antibodies, in a form allowing         its administration to a human or animal mammalian organism, and         optionally its prior culture, the said cell being genetically         modified in vitro by at least one nucleic acid sequence         containing at least one gene encoding in vivo at least one         polypeptide or one polypeptide fragment of the invention or         encoding at least one molecule inhibiting the function and/or         the binding and/or the expression of at least one polypeptide or         of one polypeptide fragment of the invention or encoding at         least one antibody or one antibody fragment capable of binding         to at least one polypeptide or a polypeptide fragment of the         invention;     -   a genetically modified cell, in particular chosen from         eukaryotic cells, such as COS and CHO cells and lower eukaryotic         cells, such as yeast cells, in particular cells derived from         Saccaromyces cerevisiae and Pichia pastoris, transformed with at         least one nucleic acid sequence or a nucleotide fragment or a         DNA molecule or by a vector of the invention; and     -   a pharmaceutical or vaccine composition comprising such a cell.

The pharmaceutical compositions defined above are DNA vaccine compositions which are particularly advantageous, in particular compared with “conventional” vaccine compositions based on a recombinant protein. Indeed, the use for vaccine purposes of recombinant proteins is a cumbersome and expensive system, in particular because it requires very important steps of purification of recombinant antigens. Furthermore, one of the difficulties encountered is of obtaining a sufficiently long persistence of the vaccine to maintain good immune memory. By contrast, the DNA vaccination method, whose advantages are inherent in the intrinsic properties of the DNA, is simple and not very expensive and is simply carried out by intramuscular or intradermal injection. Furthermore, it should be noted that:

-   -   DNA vaccines are noninfectious/nonreplicative,     -   because the immunization with DNA is a form of in vivo         transfection, the viral antigen is expressed in the mammalian         cells in its native conformation,     -   as in the case of a viral infection, a high immune response,         both humoral and cellular, is induced, and     -   furthermore, DNA vaccines can be easily combined because of         their physicochemical homogeneity.

BRIEF DESCRIPTION OF THE DRAWINGS

The figure labeled “FIGURE, ELISA 1/50” show the results of an ELISA assay to detect anti-HXHV antibodies in 8 control samples and 16 patient samples.

I. MATERIALS AND METHODS I-1. Source of Biological Material

The material used for the RDA consists of sera archived in a serum bank. The RDA was applied to a case of serious hepatitis of unknown aetiology, successfully treated with IFN. The normalization of the transaminases in this patient after antiviral treatment and especially the relapse after stopping the treatment, with another response during reintroduction of the treatment are elements which militate in favour of a viral aetiology of the disease. A serum sample before treatment and a serum sample after treatment were used for the RDA, the sample before treatment potentially containing the HXHV virus and the sample after treatment few or no viruses.

I-1.1 Preliminary Search for Known Hepatitis Viruses

Screening by Ultrasensitive PCRs:

In order to eliminate the presence of known hepatitis viruses, which could be present in very low quantities or in the form of mutants, very sensitive PCR tests for the hepatitis viruses responsible for chronic hepatitis (B, C, G and TTV) were developed (Chemin et al, J of Hepatol., 2001) which were highly sensitive (detection of 10 viral genomes).

The successive sera from the patient treated with interferon and intended for the subtractive hybridization method remained negative by these tests for all known hepatitis viruses and for the SEN virus (Minoru Shibata et al. The Journal of Infectious Diseases 2001; 184:400-404).

I-1.2 Choice of the Samples for the RDA Procedure

Tester samples or positive controls at the transaminase peak: total nucleic acids extracted from the serum collected at the transaminase peak.

Driver samples or negative controls after treatment: total nucleic acids extracted from the serum collected at the lowest transaminase level.

The extractions of the nucleic acids are carried out with the QIAGEN QIAamp® Viral RNA Mini Kit. The differential technique is carried out using the CLONTECH PCR—Select™ cDNA Subtraction Kit from CLONTECH according to the manufacturer's instructions.

I-2. RDA Procedure

I-2.1 Principle

The method developed by Lysitsyn et al. in 1993 is based on the following principle and the Clontech kit (Clontech PCR-select™ cDNA substraction kit) was used:

Reduction of the Complexity of the Genomic DNA.

The 1st step of the RDA consists in reducing the complexity of the genome. For that, it is necessary to use a restriction enzyme which has a fairly frequent cleavage site, making it possible to reduce the complexity of the genome. The result of this step is the production of a set of sequences of lesser complexity although representative of the initial sequences, hence the term “representational”. The preliminary reduction of the complexity of the genome to be studied improves the efficiency of the enrichment steps by facilitating the complete hybridization of the samples.

Enrichment

Adaptors are joined (by means of a ligase) to each end of the DNA fragments of the tester sample containing the viral genome. The driver sample has no adaptors.

During the subtractive hybridization, the tester is exposed to an excess of driver. The driver D contains numerous DNA fragments in common with the tester T and therefore plays the role of competitive inhibitors by limiting self-hybridization of the DNA fragments of the tester common to the two populations.

The whole is subjected to a process of denaturation/renaturation during which three types of association will be produced according to the complementarity of the sequences.

The driver being in a large excess, the fragments common to both pools form mainly D/D hybrids (without adaptors) and also T/D hybrids (with an adaptor at the end of one of the two strands). Only the T/T hybrids possess at each end the adaptors which will be supplemented during the extension step preceding the PCR. By repeating the procedure several times after having selected the T/T duplexes, it is theoretically possible to purify the sequences present only in the tester. However, the efficiency of the subtrative hybridization technique is partly limited because of the great complexity of the human genome and of the abundance of genomic DNA sequences in any serum sample. The repetition of subtractive step results in a final enrichment factor of 10² to 10³, whereas a factor of 10⁶ is sought.

It is therefore necessary to combine this method with a second so-called kinetics enrichment method. This is carried out by means of a PCR step which uses primers complementary to the adaptors added during the preceding step. The T/T duplexes are therefore exponentially amplified by PCR and the T/D duplexes undergo a linear amplification in which the derived fragments are single-stranded. The T/D hybrids are, for their part, not amplified. It is possible to destroy the single-stranded DNAs with a nuclease which spares the double-stranded DNAs. This method of selective enrichment of the double-stranded testers can be repeated with different adaptors in order to enrich the target DNA with respect to the other sequences of the tester after amplification. In general, three cycles of this reaction make it possible to obtain the enrichment factor of 10⁶ for the viral sequence to be sought. Subsequently, the products obtained are subcloned into a plasmid for sequencing and analysis.

I-2.2 Protocol

The RDA is carried out on the tester and driver samples using the DNAs from the patient previously mentioned.

Digestion of the Samples with the Restriction Enzyme RsaI

The procedure is carried out separately for the DNA of the tester and the DNA of the driver.

In order not to miss any lane, an RDA experiment was carried out in parallel with the RNAs on the same samples. However, no clones, whose sequence does not exhibit homology with known sequences, was able to be obtained from the viral RNA.

Preparation of the Following Mixture:

The mixture 10× RsaI buffer (5 μl), RsaI (10 U/μl) (1.5 μl), 43.5 μl nucleic acids (2 μg) is prepared. The mixture is incubated for 1 h 30 min at 37° C. and the reaction is stopped with 2.5 μl of 20× EDTA/glycogen. An extraction is carried out with 50 μl of phenol:chloroform:isoamyl alcohol (25:24:1). A centrifugation is carried out for 10 min at 14 000 rpm and the top aqueous phase is collected. Another extraction is carried out with 50 μl of chloroform:isoamyl alcohol (24:1), followed by a centrifugation for 10 min at 14 000 rpm and collection at the top aqueous phase. The aqueous phase is precipitated with 25 μl of 4M NH₄OAc and 187.5 μl of 95% ethanol, followed by centrifugation for 20 min at 14 000 rpm and removal of the supernatant. The pellet is washed with 200 μl of 80% ethanol. Another centrifugation is carried out for 5 min at 14 000 rpm and the supernatant is removed. The pellet is air-dried for 5 to 10 min and then dissolved in 5.5 μl of H₂O.

Ligation of the Tester to the Adaptors (which Contain the Sequences of the PCR Primers Necessary for the Final Phase of the Procedure):

1 μl of the tester is diluted in 5 μl of water. The ligation mixture is prepared as follows: H₂O (15 μl), 5× ligation buffer (BIOLABS) (10 μl), T4 DNA ligase (400 U/μl) BIOLABS (5 μl).

The mixture 1.1 was prepared as follows: tester 2 μl, adaptor 1 (10 μM) 2 μl, Master mix 6 μl.

The mixture 1.2 was prepared as follows: tester 2 μl, adaptor 2R (10 μM) 2 μl, Master mix 6 μl.

Preparation of the nonsubtracted control: 2 μl of the mixture 1.1 were added to 2 μl of the mixture 1.2. The mixture thus prepared is incubated overnight at 16° C. and the reaction is stopped by adding 1 μl of 20× EDTA/glycogen. The ligase is inactivated at 72° C. for 5 min and the mixture is cooled in ice.

Subtractive Hybridization: Tester—Driver.

The procedure is carried out separately for the DNA of the tester and the DNA of the driver.

First Hybridization:

Two mixtures H1 and H2 were prepared separately, consisting of the DNA of the tester ligated to the adaptor 1 (mixture H1) or the adaptor 2R (mixture H2). Mixture H1: driver 1.5 μl, “tester 1-1” 1.5 μl, 4× hybridization buffer 1 μl. Mixture H2: driver 1.5 μl, “tester 1-2” 1.5 μl, 4× hybridization buffer 1 μl. Oil was added to each of these mixtures and each mixture is incubated for 1 min 30 sec at 98° C. then for 6 h at 68° C. before immediately proceeding to the second hybridization.

Second Hybridization:

The following mixture is prepared: driver 1 μl, 4× hybridization buffer, 1 μl, H₂O 2 μl.

1 μl of the mixture is denatured at 98° C. for 1 min 30 sec.

15 μl of the mixture H2 are collected at the oil/sample interface. The air is aspirated, the driver is collected and the whole is added to the mixture H1. The whole is incubated at 68° C. overnight.

Dilution of the Subtracted DNAs:

To the hybridized tubes are added 200 μl of dilution buffer. The mixture, after aspirations and dischargings, is incubated at 68° C. for 7 min and the reaction is stopped in ice.

PCR on the RDA Products

The procedure is carried out separately on:

-   -   the RDA products derived from DNAs,     -   the nonsubtracted control, the subtracted control from the kit         and the positive PCR control from the kit.

First Round of PCR:

The following mixture is prepared: H₂O 19.5 μl, 10× PCR buffer 2.5 μl, dNTPs (10 mM of each) 0.5 μl, PCR primer 1 (10 μM) 1 μl, 50× advantage cDNA polymerase mix 0.5 μl, RDA samples 1 μl.

The programme used is the following: 75° C. 5 min, 94° C. 30 sec

Then 25 cycles: 94° C. 10 sec, 66° C. 30 sec, 72° C. 1 min 30 sec

Second Round of PCR:

Use of 1 μl of first PCR product: the same mixture is used.

20 cycles are performed: 94° C. 10 sec, 68° C 30 sec, 72° C. 1 min 30 sec.

The pairs of primers of the Clontech PCR-select™ cDNA subtraction kit are used, they are located in the adaptors “linked” to the tester DNA at the beginning of the RDA procedure.

Analysis of 8 μl of sample on 1% agarose gel in 1× TBE with an ethidium bromide staining.

The RDA products are then ligated into the plasmid pTOPO using topoisomerase I, and then cloned into E. coli using the Invitrogen TOPO TA Cloning® Kit.

II. ANALYSIS OF THE RDA PRODUCTS II-1. Screening of the Clones Generated by RDA

The RDA technique makes it possible to obtain, from tester and driver samples, PCR products which reflect what is potentially different between the two samples. This constitutes the material subtracted.

After cloning of the RDA products, 643 clones were screened according to the steps described below.

II-2. Replicas of the Products of Cloning

In order to remove a maximum of clones of human origin, the replicas of the “DNA” RDA clones are hybridized with probes corresponding to human genomic DNA digested with EcoRI/PstI and radiolabelled with ³²P.

The results at the end of this screening are presented below.

II-3. Interrogation of Data Banks

The fifty clones selected at the end of the first step are sequenced. Their respective sequences are compared to the known sequences in the data banks Swissprot, Embl, Genbank, Draft of the human genome. A number which are unknown appear. The results of the distribution of the sequences are given below.

Phosphatase 23% Human DNA chromosomes 16 + 17 31% Proteinase 8% Human immunoglobulin 16% Unknowns 8%

II-4. Additional Screening

Additional screening steps were carried out on the 4 clones selected in the preceding step according to the process described below.

-   -   Dot blot on the DNA of the clones selected using an EcoRI/PstI         genomic DNA probe radiolabelled with ³²P.     -   Southern blot of genomic DNA using, as probe, the clones         previously selected, labelled with ³²P.

At the end of these various steps, two “DNA” clones, whose sequences are unknown in the data banks, were selected.

The following step is the validation of the relevance of these data both to the samples obtained from patients suffering from hepatitis of undetermined aetiology and the controls consisting, on the one hand, of blood donors and, on the other hand, of patients suffering from pathologies of the liver of nonviral origin. For that, primers were synthesized within the DNA of the two clones and PCRs were performed using these primers on the genomic DNA extracted from the serum of blood donors in order to eliminate the possibility of the DNA of the clones corresponding to a DNA sequence which is frequent in the human genome.

One clone containing an insert of 1400 bp (XH) obtained from the RDA on the DNA was selected for its lack of homologies with the human genomic DNA and with any sequence present in the databases.

This sequence, rich in GC (62%) has several open reading frames. It is identified in SEQ ID NO: 1. The open reading frames are identified in SEQ ID NO: 2, 3, 4 and 5.

III. CHARACTERIZATION OF THE SEQUENCE ASSOCIATED WITH HEPATITIS X:XH

Four parallel approaches were used in order to characterize and specify the nature of the XH sequence isolated:

-   -   Bioclinical and epidemiological studies     -   “Molecular” approach     -   Production of specific antibodies     -   Electron microscopy study

III-1. Bioclinical and Epidemiological Studies

-   -   Different sets of primers and probes were synthesized in order         to be able to amplify by PCR the XH sequence.

It is possible to use the following combination of primers:

Sense primer (1M13): 5′-CCCGCCCCGCTGATGAAAAG-3′ (SEQ ID NO: 10) Anti-sense primer (3T7): 5′-ATGCCAACGCCCAGAGTCCG-3′ (SEQ ID NO: 13)

PCR cycles: 75° C. 5 min, 94° C. 2 min, 94° C. 10 s×28, 66° C. 30 s×28, 72° C. 1 min 30×28 and 72° C. 7 min.

Second round of PCR:

3 μl of samples from the 1^(st) round were diluted with 27 μl of water.

The following mixture was prepared: H₂O 17.5 μl, 10× PCR buffer 2.5 μl, dNTPs (10 μM of each) 0.5 μl, nested PCR sense primer (10 μM) 1 μl, nested PCR anti-sense primer 2R (10 μM) 1 μl, 50× advantage cDNA polymerase mix 0.5 μl, RDA samples 1/10 2 μl.

The following pairs of primers were used:

Sense primer (1M13): 5′-CCCGCCCCGCTGATGAAAAG-3′ (SEQ ID NO: 10) Anti-sense primer (1T7): 5′-GATGTTTCTGTGTCTGTGGG-3′ (SEQ ID NO: 14)

PCR cycles: 94° C. 2 min, 94° C. 10 s×10-15, 68° C. 30 s×10-15, 72° C. 1 min 30×10-15 and 72° C. 7 min.

First of all, 90 blood donors having normal transaminases were screened by PCR. All are negative for the XH sequence.

-   -   In parallel, the presence of the XH sequence at different dates         in the serum of the patient having made it possible to carry out         the RDA was sought. The presence of the XH sequence was observed         only at the time when the transaminases were particularly high.         Analysis of a liver biopsy from this patient after the fall in         the transaminases reveals the presence of this sequence. It         should be noted, in this case, that the patient has now been         treated with interferon for 10 years and that any attempt to         stop the treatment has as a consequence a rapid increase in the         transaminases, suggesting the persistant presence of the agent         implicated in the liver disease.     -   Twenty cases of primary biliary cirrhosis also remained negative         for the XH sequence in the serum and the liver. Four cases of         drug-induced hepatitis were also studied and also proved         negative. Only 1/21 cases of autoimmune hepatitis and 1/7 cases         of alcoholic hepatitis were positive for the XH sequence. These         results on control populations made it possible to verify that         the XH sequence is not usually present in “normal” human serum         or in the context of liver lesions of nonviral aetiology.     -   Very advantageously, the analysis of liver and serum samples         from patients of the Hôtel Dieu in Lyon, suffering from a         chronic non-A, non-E hepatitis, made it possible to observe that         10% of them (11/109) are carriers of the XH sequence. A similar         percentage of patients positive for the HXHV DNA is obtained in         Moroccan patients having a chronic non-A, non-E hepatitis.     -   The patients positive by PCR in the serum for the XH sequence         also appeared positive for the DNA extracted from liver biopsies         when the biopsy was available. The presence of the XH sequence         was able to be observed at different dates, several years apart,         for the same patient.     -   Product amplified by PCR which were sequenced and show a very         similar sequence from one patient to another.     -   These patients all have a chronic hepatitis with varying degrees         at the level of the liver lesions, from minimal hepatitis to         cirrhosis. Only some received blood transfusions, which         constitutes a clearly established risk factor as for the         transmission of the hepatitis virus. As these patients were not         carriers of any known hepatitis virus, they were not subjected         to any antiviral treatment protocol.     -   Furthermore, analysis of the thirteen cases of acute non-A,         non-E hepatitis from Brazil allowed us to detect the presence of         the XH sequence in eleven of these patients in the acute phase.

III-2. “Molecular” Approach

In order to determine the nature of the DNA isolated (single-stranded or double-stranded), the XH sequence was captured with alternately two oligonucleotides specific for either of the two DNA strands of the XH sequence attached to magnetic particles (Gene Trapper cDNA positive selection system, Gibco BRL (trade name)). The oligonucleotides used are the following:

sense oligonucleotide S6M13: 5′-GCCATGTAACTCGGCAGTGC-3′ (SEQ ID NO: 9) antisense oligonucleotide Comp S6M13: 5′-GCACTGCCGAGTTACATGGC-3′ (SEQ ID NO: 15)

In a second instance, the products released after capture with the specific oligonucleotides are analysed by:

-   -   PCR and hybridization of the PCR products with a probe specific         for XH.     -   Cloning, analysis of the clones by PCR, hybridizations of the         replicas of the cloned products, sequencing of the clones.

This approach was validated on the XH sequence cloned into the TOPO vector. In this form, the sequence derived from the RDA is double-stranded since it is derived from a PCR. The capture procedure carried out on the cloned sequence finally makes it possible to capture the two DNA strands present.

The nature of the XH sequence which circulates in the patients was examined using several sera of “hepatitis X” patients, who were positive by PCR for the XH sequence. The sera are ultracentrifuged or not before the capture procedure.

All of these results demonstrate that only one of the oligonucleotides (the sense oligonucleotide, S6M13) is capable of retaining the XH sequence which circulates in the serum of the patients. Consequently, this sequence is at least partially single-stranded. This hypothesis on the single-stranded nature of the XH DNA is supported by trials of preliminary treatments of the XH DNA with S1 nuclease, an enzyme which is specific for the single-stranded forms of DNA. Preliminary treatment of extracts of sera positive for XH DNA abolishes the PCR signal and therefore confirms the single-stranded nature of the sequence.

III-3. Production of Specific Antibodies

-   -   The XH sequence (SEQ ID NO: 1) has four open reading frames.         ORF1 is presented in SEQ ID NO: 2, it comprises 101 amino acids         encoded by bases 1 to 103 of SEQ ID NO: 1. ORF2 is presented in         SEQ ID NO: 3, it comprises 135 amino acids encoded by bases 829         to 1233 of SEQ ID NO: 1. ORF3 is presented in SEQ ID NO: 4, it         comprises 135 amino acids encoded by bases 270 to 674 of SEQ ID         NO: 1. ORF4 is presented in SEQ ID NO: 5, it comprises 183 amino         acids encoded by bases 813 to 1361 of SEQ ID NO: 1. By computer         analysis, it was shown that the protein selected possesses a         region of 14 amino acids which has all the immunogenicity and         hydrophilicity properties required to induce the production of         antibodies.     -   A polypeptide corresponding to the abovementioned region of 14         amino acids was synthesized for the production of polyclonal         antibodies. The sequence of this polypeptide is given below and         identified by a reference in SEQ ID NO: 6.

RRAAELHRRDQYRL

For the immunization of the rabbits, a cysteine (C) was added to the COOH-terminal end of this polypeptide for coupling to BSA. The immunogen RRAAELHRRDQYRLC-BSA was injected into rabbits in an amount of 100 μg of immunogen per rabbit and per injection. The immunization protocol used is the following:

D0: 1st taking of 10 ml of blood, immunization: 0.1 mg of immunogen (1 mg/ml)+0.4 ml of physiological saline+0.5 ml CFA 1 ml ID (0.1 ml×10)

D28: 0.1 mg of immunogen (1 mg/ml)+0.4 ml of physiological saline+0.5 ml IFA ID-1 ml ID (0.1 ml×10)

D56: 0.1 mg of immunogen (1 mg/ml)+0.4 ml of physiological saline+0.5 ml IFA-1 ml SC (0.25 ml×4)

D63: 1st taking of 3 ml of blood from the ear without anticoagulant

D84: 0.1 mg of immunogen (1 mg/ml)+0.4 ml of physiological saline+0.5 ml AFI 1 ml IM (0.25 ml×4)

D91: 2nd taking of 9 ml of blood from the ear without anticoagulant

D112: 0.1 mg of immunogen (1 mg/ml)+0.4 ml of physiological saline+0.5 ml IFA-1 ml ID (0.1 ml×10)

D119: 3rd taking of 9 ml of blood from the ear without anticoagulant.

The production of specific antibodies is a very effective tool for screening for the expression of the XH sequence on biopsies from non-A, non-E patients in parallel with other categories of patients or controls.

-   -   The polypeptide of 14 amino acids (SEQ ID NO: 6) is used to         develop an ELISA test for the capture of antibodies specific for         the HXHV virus potentially present in patients having a chronic         non-A, non-E hepatitis. Into the wells of a microtitre plate are         deposited 100 μl of streptavidin diluted 1/100 in carbonate         buffer. The deposition is followed by incubation for 2 hours at         37° C. in an incubator, after which three washes are carried         out. 100 μl of biotinylated peptide, diluted 1/100 in PBS, are         then added to each of the wells. The mixture is incubated         overnight at 40° C. Three washes are then carried out. 250 μl of         PBS+goat serum are then added in order to saturate the sites.         The whole is incubated for 2 hours at 37° C. After three washes,         100 μl of each serum to be tested (diluted at the appropriate         dilution in PBS Tween+SC) are added and an incubation is carried         out for 2 hours at 37° C. in an incubator. Three washes are then         carried out and 100 μl of a dilute solution of anti-human IgG         antibody coupled to peroxidase are deposited. The whole is         incubated in an incubator for one hour at 37° C. Incubation is         followed by a step of three washes. The visualization is carried         out by adding ortho-phenylenediamine (100 μl). The reaction is         blocked by adding 50 μl of H₂SO₄ and the reading is carried out         at OD 492 nm and 635 nm. The results are presented in the         appended figure. As is evident from this figure, 6 patients are         very well detected by this technique among the 16 in whom the XH         sequence had been detected by PCR. The seventh patient is weakly         detected, at the limit of the threshold.

III-4. Electron Microscopy Study

Sucrose gradients were prepared in order to isolate possible viral particles associated with the presence of the XH sequence. For that, the serum of a patient of the non-A, non-E hepatitis cohort was used. Two consecutive fractions of this gradient appeared positive by PCR for the XH sequence. These fractions correspond to densities of the order of 1.2 to 1.5 g/cm³. The electron microscopy study made it possible to observe particles whose size and regularity (110 nm diameter) are compatible with that of a viral agent. The frequency with which these particles are observed in electron microscopy suggests a concentration of the order of 5×10⁵ particles/ml of serum. The ELISA test developed allowed us to search for the presence of “anti-XH” antibodies in blood donors and in various categories of patients.

IV. STUDY OF BLOOD DONORS AND PATIENTS IV-1. Search for Anti-XH Antibodies

The search for anti-XH antibodies in blood donors and in various categories of patients was carried out by the ELISA test. The results are presented in the table below.

TABLE Blood donors Patients TN TE VHC+ VHB+ HIV+ Non-A–E* Non-A–E** H* H** Total 408 389 45 40 31 44 13 47 41 number studied % of 1.22 6.2 3 16 35 23 31 36 17 anti-XH positives TN means “blood donors having a normal transaminase level” TE means “blood donors having a high transaminase level” HCV+ means “HCV-positive patients” HBV+ means “HBV-positive patients” HIV+ means “HIV-positive patients” Non A–E* means “patients suffering from a chronic non-A–E hepatitis” Non A–E** means “patients suffering from a fulminant non-A–E hepatitis” H* means “haemophilic patients who received blood transfusions before 1987, that is to say before treating blood with detergent solvents” H** means “haemophilic patients who received blood transfusions after 1987”

The difference in prevalence of the anti-XH antibodies between the 408 blood donors having normal transaminases and the 389 blood donors having high transaminases is significant. This difference, observed between these two groups tested according to a double blind design, suggests a causal relationship between the presence of the anti-XH antibodies and the hepatic disease. A fraction of the blood donors having high transaminases (20%) is found to be positive by PCR for the XH sequence. This sequence was never found in the blood donors having normal transaminases.

A higher percentage of positivity in anti-XH antibodies is found for the HIV-positive patients (35%), compared to the 16% in the patients who are chronic carriers of HBV and to the 3% in the chronic carriers of HCV. Detailed study of the risk factors to which the patients were exposed demonstrates that the XH sequence is transmissible by the parenteral and sexual route.

Only the patients having a chronic or fulminant non-A, non-E hepatitis positive in ELISA are positive by PCR in 50% of the cases, whereas no positive for DNA was detected in the HCV or HBV group of patients or among the haemophiliacs.

A study was also carried out on patients suffering from acute hepatitis of unknown aetiology progressing to chronicity or cure. Of 13 cases studied, 11 proved positive for anti-XH antibodies during the acute phase of the disease. Among the cases which were able to be monitored, all remained positive for antibodies during this time.

IV-2. Search for the XH Sequence by PCR

A real-time quantitative PCR method using the Roche® Light cycler was developed in order to amplify the XH sequence. It was used, inter alia, to amplify the XH sequence in the ORF 4 in the 11 patients who were found to be positive for anti-XH antibodies.

The four specific primers described below were synthesized and purified by HPLC.

S1 (sense): 5′-GCGTTGTGGTTCTGTTGC-3′ (SEQ ID NO: 19) S2 (sense): 5′-GATCAATATCGCCTACGC-3′ (SEQ ID NO: 20) AS1 (anti-sense): 5′-CTGAAGGATAGGGCTGATG-3′ (SEQ ID NO: 21) AS2 (anti-sense): 5′-CTGTTCGCCAGCCACCAG-3′ (SEQ ID NO: 22)

The PCR is carried out using a Qiagen® kit “QuantiTect SYBR Green PCR Kit” (trade name).

The composition of the reaction mixture is the following

Master mix quantitect Qiagen 10 μl Sense primer (15 μM)  1 μl Anti-sense primer (15 μM)  1 μl Target DNA  5 μl Water (without RNAse)  3 μl Total volume per capillary tube 20 μl

Once the 20 μl have been depositied, the capillary tubes are sealed, briefly centrifuged and placed in the rotor of the Light Cycler.

PCR Protocol

Activation:

-   95° C. for 15 minutes.

Amplification/quantification:

-   Number of cycles 45

Denaturation Annealing Extension Temperature [° C.] 95 52 72 Incubation [s] 0 5 Tx* Level of temperature 20 20 20 transition [° C./s] Tx*: temperature depending on the combination of primers used.

Primers Size of the amplicon (bp) Tx (s) S1/AS1 441 18 S1/AS2 312 13 S1/AS2 331 13 S2/AS2 232 10

Analysis of the Melting Curve:

Denaturation Annealing Extension Temperature [° C.] 95 40 95 Incubation [s] 0 5 0 Level of temperature 20 20 0.3 transition [° C./s]

Cooling:

-   40° C. for 30 seconds.

Characterization of the Threshold for Detection of the Sequence of Interest

The theoretical detection threshold for the XH sequence inserted into the plasmid is between 1 and 2 copies per capillary tube. The Tm of the amplicon S1/AS2 (312 bp) most frequently used is 88° C.

The application of this technique shows, inter alia, that four out of five of the patients who progressed to a chronic hepatitis are positive by PCR for the XH sequence. Conversely, five out of six of the patients who were cured became negative by PCR for the XH sequence. 

1. An isolated DNA nucleotide fragment, comprising a nucleotide sequence of at least 40 contiguous nucleotides belonging to the segment starting at nucleotide 813 and ending at nucleotide 1361 of the sequence set forth in SEQ ID NO: 1, or the complementary sequence of said segment.
 2. An isolated DNA nucleotide fragment, comprising a nucleotide sequence of at least 40 contiguous nucleotides belonging to the segment starting at nucleotide 927 and ending at nucleotide 968 of the sequence set forth in SEQ ID NO: 1, or the complementary sequence of said segment.
 3. An isolated DNA nucleotide fragment, comprising the sequence set forth in SEQ ID NO: 1 or its full-length complementary sequence.
 4. An expression cassette, which is functional in a cell derived from a prokaryotic or eukaryotic organism, allowing the expression of a nucleic acid sequence according to claim 1, placed under the control of elements necessary for its expression.
 5. A vector comprising an expression cassette according to claim
 4. 6. An isolated cell derived from a eukaryotic or prokaryotic organism comprising an expression cassette according to claim
 4. 7. Cell according to claim 6, derived from a eukaryotic organism chosen from COS cells or CHO cells.
 8. Cell according to claim 6, derived from a lower eukaryotic organism chosen from Saccharomyces cerevisiae cells or Pichia pastoris cells.
 9. A method for preparing a polypeptide, comprising culturing a host cell as defined in claim 6 in an appropriate culture medium, obtaining said polypeptide and purifying said polypeptide to the required degree of purity.
 10. A primer or probe capable of hybridizing with a nucleic acid sequence as defined in claim 1, wherein the primer or probe is chosen from any one of the sequences SEQ ID NOS: 19-22.
 11. A diagnostic composition, comprising at least one probe or one primer as defined in claim
 10. 12. A method of detecting HXHV DNA or RNA in a biological sample, comprising: (i) Contacting a sample suspected of containing HXHV nucleic acid with at least one probe or primer comprising 12 or more contiguous nucleotides of the segment of nucleotides 813-1361 of SEQ ID NO: 1 or the complement thereof, and then (ii) demonstrating hybridization of said probe or primer to said HXHV DNA or RNA or amplification of said HXHV DNA or RNA, wherein demonstration of said hybridization or amplification indicates the presence of HXHV DNA or RNA.
 13. A vector comprising a nucleotide sequence encoding: (i) Either at least one polypeptide or polypeptide fragment encoded by a DNA nucleotide fragment according to claim 1, or (ii) an antibody or a binding fragment thereof capable of binding to at least one polypeptide of polypeptide fragment as defined in (i).
 14. An immunogenic composition comprising a vector as defined in claim 13, wherein said nucleotide sequence is placed under the control of elements ensuring its expression in vivo.
 15. An isolated genetically modified eukaryotic cell transformed with a DNA nucleotide fragment according to claim
 1. 16. An immunogenic composition comprising a cell as defined in claim
 15. 17. A transformed cell of claim 15 which is derived from one of the following types: COS or CHO cell-lines or Saccharomyces cerevisiae or Pichia pastoris cells.
 18. The immunogenic composition of claim 16, wherein the cell is derived from one of the following types: COS or CHO cell-lines or Saccharomyces cerevisiae or Pichia pastoris cells. 